Embodiments of the inventive concept relate generally to semiconductor memory devices. More particularly, embodiments of the inventive concept relate to nonvolatile memory devices comprising a one-time-programmable lock bit register.
Semiconductor memory devices can be roughly divided into two categories according to whether they retain stored data when disconnected from power. These categories include volatile memory devices, which lose stored data when disconnected from power, and nonvolatile memory devices, which retain stored data when disconnected from power.
Examples of volatile memory devices include static random access memory (SRAM), dynamic random access memory (DRAM), and synchronous DRAM (SDRAM). Examples of nonvolatile memory devices include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable PROM (EEPROM), flash memory, phase-change random access memory (PRAM), magnetic random access memory (MRAM), resistive random access memory (RRAM), and ferroelectric random access memory (FRAM).
Among nonvolatile memory devices, flash memory has achieved increasing popularity in recent years due to a variety of attractive features, such as relatively high storage capacity and performance, and relatively low power consumption and cost. Recently, however, PRAM has been proposed as a potential alternative to flash memory. PRAM, also known as an Ovonic Unified Memory (OUM), is a type of variable-resistance memory.
A PRAM typically comprises a one-time-programmable (OTP) block that stores security data such as a serial number, information regarding a vendor, and a date of manufacture. The security data is sensitive information and must be secured against external interference such as unwanted tampering or reprogramming. However, unlike many flash memory devices, conventional PRAMs do not have a specific memory block designed for one time programming and subsequent data protection. As a result, security data stored in an OTP block of a conventional PRAM may be vulnerable to external interference.